In the past, in order to facilitate removal of gases and hydrocarbons from existing formations, inclined or deviated wellbores have been used with greater frequency to improve productivity. Completions in such wellbores have been problematic in certain applications. For instance, traditional methods of running casing and cementing it present difficulties when the wellbore is almost horizontal. It is difficult to obtain uniform coverage of the cement when the wellbore is deviated. This occurs because gravity works to force the cement downwardly so that if the entire annulus is not sufficiently filled, the integrity of the cementing job is jeopardized or lost. Additionally, even if it were possible to reliably cement casing in a deviated wellbore, a subsequent step of perforating must also occur.
Prior designs have employed slotted or otherwise pre-perforated liners which are simply placed in the deviated segment of the wellbore. The production from the formation occurs through the slotted casing. Frequently, if the formation is unconsolidated, the slotted casing may plug. Similarly, any screens installed on the bottom of the production tubing installed into the casing may also plug if the movement of fluid brings with it a large amount of solids into the screen area.
While gravel-packing is a technique that has been used in the past to eliminate screen blockages and to facilitate production, many techniques of gravel-packing which work quite well in vertical wellbores become problematic in deviated wellbores. Again, the distribution of the gravel-packed material completely around a screen is more difficult to accomplish in place in a deviated wellbore due to the effects of gravity.
As an alternative to slotted casing, pre-packed screens that have already affixed to them a layer or layers of gravel or other granular materials have been used. However, in situations where the formation is unconsolidated and large amounts of solids are produced, even pre-packed screens exhibit clogging and undue pressure drops, thereby diminishing the productivity of the well.
Accordingly, it is desirable to provide a one-trip method which can eliminate the need for casing which must be perforated if cemented in a deviated wellbore. Additionally, it is desirable to create a system involving few steps, the end result of which will be the proper placement of screens which can be made ready for production upon the opening of sleeve-type valves. Additionally, the method of the invention places a permeable, settable material on the outside of the screens to facilitate production from the formation while decreasing the prospects of clogging of the screens. Finally, a method would be desirable which isolates the cement which is ultimately used from the permeable material which is in the annular space outside the screens. These objectives and others have been accomplished by the apparatus and method of the present invention as will be outlined below.